E-paper printing system

ABSTRACT

An e-paper printing system comprising a set of electrodes comprising a number of electrodes to erase a portion of e-paper as the e-paper moves relative to the set of electrodes in which the set of electrodes causes a first electric field to be applied to the e-paper with a magnitude of the first electric field increasing at a first rate sufficiently high to cause the erasure of the portion of the e-paper, and causes a second electric field to be applied to the e-paper with a magnitude of the second electric field decreasing at a second rate that is sufficiently low to preserve the erasure of the portion of the e-paper.

BACKGROUND

Electronic paper (“e-paper”)is a display technology designed to recreatethe appearance of ink on ordinary paper. E-paper reflects light likeordinary paper and may be capable of displaying text and imagesindefinitely without using electricity to refresh the image. This may beaccomplished while still allowing the image to be changed later. E-papercan also be implemented as a flexible, thin sheet, similar to paper. Bycontrast, a flat panel display does not exhibit the same flexibility,uses a backlight to illuminate pixels, and constantly uses power duringthe display. E-paper implementations, such as electronic books(“e-hooks”), include an e-paper display and electronics for renderingand displaying digital media on the e-paper.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various examples of the principlesdescribed herein and are a part of the specification. The examples donot limit the scope of the claims.

FIG. 1 is a block diagram of an e-paper printing device according to oneexample of the principles described herein.

FIG. 2 is a block diagram of an e-paper printing device according toanother example of the principles described herein.

FIG. 3 depicts a waveform used as an erase pulse and is applied to theelectrodes as the e-paper is passed through the printing device of FIGS.1 and 2 according to one example of the principles described herein.

FIG. 4 is a block diagram of an apparatus used to test the e-paper ofFIGS. 1 and 2 according to one example of the principles describedherein.

FIG. 5 depicts a waveform used as a write and erase pulse and is appliedto the electrodes as the e-paper is passed through the printing deviceof FIGS. 1 and 2 according to one example of the principles describedherein.

FIG. 6 is a flowchart showing a method of erasing e-paper according toone example of principles described herein.

FIG. 7 is a flowchart showing a method of erasing e-paper according toanother example of principles described herein.

FIG. 8 is a flowchart showing a method of manufacturing an e-papererasure device according to one example of the principles describedherein.

Throughout the drawings, identical reference numbers designate similar,but not necessarily identical, elements.

DETAILED DESCRIPTION

As described above, e-paper is used in a variety of display applicationssuch as signage, e-books, tablets, cards, posters, and pricing labels.E-paper has several paper-like features. For example, e-paper is areflective display that uses ambient light as an illumination source.The ambient light strikes the surface and is reflected to the viewer.The usage of pigments similar to those which are used in printing allowsthe e-paper to be read at a vide range of angles and lightingconditions, including full sunlight. The use of ambient light alsoreduces the amount of power used in connection with the e-paper insteadof constantly having power produced by a device. This also minimizes theamount of energy consumed through the use of the e-paper. E-paper doesnot use energy to maintain the image, and as a result, once the image iswritten, the image remains on the e-paper for an extended period of timeor until the e-paper is rewritten. Thus, an e-paper may primarily useenergy for changes of state.

E-paper is written by generating a charge on a surface in proximity to alayer of microcapsules that contain charged pigment particles. Thecharge on the surface attracts or repels the charged pigment panicles inthe microcapsules to create the desired image. The pigment particles arestable within the microcapsules after they are moved into position.However, a wide variety of methods can be used to alter the image ortext on the e-paper after it has been written. This can restrict the useof e-paper to applications that do not require the images or text to besecure against alteration.

E-paper may be erased using a negative corona discharge mechanism, Thenegative corona discharge mechanism produces a negative electricaldischarge brought on by the ionization of a fluid surrounding aconductor that is electrically energized. The negative electricaldischarge created by the negative corona discharge mechanism is directedtowards the e-paper resulting in the e-paper being erased. However, theuse of a negative corona discharge mechanism can be disadvantageous.Specifically, the negatively charged corona created by the negativecorona discharge mechanism is unstable resulting in irreproduciblee-paper marking or erasure. in addition a negatively charged coronagenerates an amount of ozone (O₃) above what a positively charged coronadoes. This may lead to potential environmental issues when operating ane-card printer that implements a negative corona discharge mechanism.

The present application, therefore, describes an e-paper printing systemcomprising a set of electrodes comprising a number of electrodes toerase a portion of e-paper as the e-paper moves relative to the ofelectrodes in which the set of electrodes causes a first electric fieldto be applied to the e-paper with a magnitude of the first electricfield increasing at a first rate sufficiently high to cause the erasureof the portion of the e-paper, and causes a second electric field to beapplied to the e-paper with a magnitude of the second electric fielddecreasing at a second rate that is sufficiently low to preserve theerasure of the portion of the e-paper.

The present application further describes method of manufacturing ane-paper erasure device comprising electrically coupling an erasingelectrode to a voltage controller; the erasing electrode to erase aportion of e-paper in which the erasing electrode is shaped to create avarying gap between a counter electrode so as to cause, during relativemotion of the e-paper to the erasing electrode a first electric field tobe applied to the e-paper with the magnitude of the first electric fieldincreasing at a first rate sufficiently high to cause the erasure of theportion of the e-paper, and at an area downstream where the firstelectric field is applied to the e-paper, a second electric field to beapplied to the e-paper with the magnitude of the second electric fielddecreasing at a second rate sufficiently low to preserve the erasure ofthe portion of e-paper.

The present application also describes a computer program product forerasing e-paper, the computer program product comprising a computerreadable storage medium comprising computer usable program code embodiedtherewith, the computer usable program code comprising computer usableprogram code to, when executed by a processor, cause a first electricfield to be applied to the e-paper by a shaped erasing electrode, inwhich the magnitude of the first electric field increases at a firstrate sufficiently high to cause the erasure of a portion of the e-paperand computer usable program code to, when executed by a processor, causea second electric field to be applied to the e-paper by the shapederasing electrode, in which the magnitude of the second electric fielddecreases at a second rate sufficiently low to preserve a the erasure ofthe portion of e-paper area.

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present systems and methods. It will be apparent,however, to one skilled in the art that the present apparatus, systemsand methods may be practiced without these specific details. Referencein the specification to “an example” or similar language indicates thata particular feature, structure, or characteristic described inconnection with that example is included as described, but may not beincluded in other examples.

FIG. 1 is a block diagram of an e-paper printing device (100) accordingto one example of the principles described herein. The e-paper printingdevice (100) may comprise a curved erasure electrode (102) comprising anumber of electrodes. Although FIG. 1 shows a curved erasure electrode(102), other examples exist where the curved erasure electrode (102) maybe formed into other shapes so as to provide a similar effect of varyinga gap between the electrode (102) and the e-paper (115). Therefore, thecurved erasure electrode (102) is merely one example.

In the example shown in FIG. 1, the curved erasure electrode includes aground electrode (105) and a charged electrode (110). Both the groundelectrode (105) and charged electrode (110) in conjunction with aconductive ground layer (130) associated with the e-paper (115) maycause a rapidly increasing electric field to be applied to the e-paper(115) using a specific voltage which will be discussed in more detailbelow. The ground electrode (105) and the charged electrode (110) may beshaped such that the timing of the field applied to the e-paper iscontrolled as the e-paper and erasure electrode (102) are moved relativeto each other. Because the rate at which the electric field changes hasan effect on the quality of erasure of the e-paper, a slow increase inthe electric field will not provide a quality erasure of the e-paper.Instead, a rapidly increasing field is applied to the e-paper. Thisrapidly increasing field is provided by the ground electrode (105) andcharged electrode (110) together. In FIG. 1, the rapidly increasingfield is applied to the e-paper as the e-paper crosses a gap between theground electrode (105) and the charged electrode (110). This rapidapplication of the electric field causes the oppositely chargedparticles in the c-paper to move either towards or away from the surface(155) of the e-paper (115) causing a previous image to be erased.

In one example, the charged electrode (110) may be negatively chargedat, for example, −2 kV. In this example, as the e-paper (115) istranslated over the erasure electrode (102) the positively chargedparticles (i.e., 150) may be attracted to the surface (155) while thenegatively charged particles (i.e., 145) are repelled from the surface(155). In another example, the charge electrode (110) may be positivelycharged at for example, +2 kV. In this example, as the e-paper istranslated over the erasure electrode (102), the positively chargedparticles (i.e., 150) may be repelled from the surface (155) while thenegatively charged particles (i.e., 145) are attracted to the surface(155). Therefore, the present example contemplates the use of a numberof combinations of negatively or positively charged, erasure electrodes(102) and particles (145, 150) that could result in the application ofone charge on the e-paper (115) resulting in the erasure of the e-paper(115).

The e-paper (115) may be comprised of a number of layers. Specifically,the e-paper (115) may be comprised of a microcapsule layer (120)sandwiched between a transparent charge receiving layer (125) and aconductive ground layer (130). In one example, the conductive groundlayer (130), microcapsule layer (120) and transparent charge receivinglayer (125) may be disposed on a substrate (135).

The transparent charge receiving layer (125) may be comprised of atransparent polymer capable of receiving on its surface a lumber ofcharged particles from a corona discharge device. The conductive groundlayer (130) may be composed of Indium-Tin Oxide (ITO), The substrate(135) can be composed of polyester, plastic, transparent MYLAR®, orother suitable material, Along with the conductive ground layer (130),the transparent charge receiving layer (125) may receive on its surfacea number of electrons in the case of a negative corona discharge deviceor a number of ions in the case of a positively corona device. As theseparticles attach to the surface of the transparent charge receivinglayer (125), the oppositely charged particles (145, 150) are attractedto them. Selectively applying a positive corona to the e-paper (115) maycause an image to be transferred to the e-paper (115).

Although FIG. 1 shows that the conductive ground layer (130) isphysically coupled to the e-paper, other examples exist where theconductive ground layer may be a separate electrode within the printingdevice (100). In this example, the conductive ground layer (130) may actas a grounded counter electrode and placed opposite the curved erasureelectrode (102). The grounded counter electrode may act as one of theset of electrodes by which the electric field applied to the e-paper iscreated. In this case, the term “grounded” is meant to be a relativeterm such that the static potential applied to the grounded counterelectrode is the relative potential to which all other potentialsapplied to all other electrodes are measured.

The microcapsule layer (120) may be comprised of a number ofmicrocapsules (140), In one example the microcapsules (140) may alignedas a single layer of microcapsules (140), In FIG. 1, each microcapsule(140) further includes both white particles (145) and black particles(150) suspended in a fluid medium. Because the white particles (145) andblack particles (150) are suspended in a fluid medium, they may bemanipulated in the presence of an electric field such that they areeither repelled away from or attracted to the surface (155) of thee-paper (115) depending on a charge associated with each type ofparticle. Ambient light is allowed to be transmitted through the chargereceiving layer (125), strike the particles (145 150), and reflect backto the viewer. As a result, when white particles (145) of a microcapsule(140) are located near the transparent charge receiving layer (125), themicrocapsule (140) appears white to a viewer. When the black particles(150) of a microcapsule (140) are located near the transparent chargereceiving layer (125) the microcapsule (140) appears black to theviewer.

Each type of particle (145, 150) may have a charge associated with it.These charged particles (145, 150) may be moved within the microcapsules(140) under the influence of an electric field or an induced current.The application of the electric field by for example, the erasureelectrode (102) creates capacitive currents (Icap=C*(dV/dt)) inside thee-paper (115). The capacitive currents are field change rate dependentand is proportional to the rate of change of applied electric field. Theparticles (145, 150), however, may experience other forces acting uponthem such as motion induced drag due to the viscosity of the solutionthe particles (145, 150) are in, the elastic forces due to the inclusionof a crosslinked polymeric matrix, the number of particles (145, 150)per unit area, among others. Each of these factors may increase ordecrease the resistance of the particles (145, 150) to change positionwithin the microcapsules (140) under the influence of the electricfield. As will be discussed below, the sharp increase in the electricfield combined with a gradual reduction in that electric field willcause the particles (145, 150) to maintain the state they were in afterthe sharp increase in the electric field. This is because a decayingresistive current is experienced by individual particles (145, 150).

In one example, tea black articles (150) may be positively chargedparticles and the white particles (45) may be negatively chargedparticles, In this example, various shades of gray can be created byvarying the arrangement of alternating microcapsules with white (145)and black (150) particles located near the charge receiving layer (125)to produce halftoning. Other examples exist where the black particles(150) are negatively charged and the white particles (145) arepositively charged.

Although, in the above description, the microcapsules (140) aredescribed to comprise black (150) and white (145) particles, any type orcolor of particles may be used. Therefore in another example, only whiteparticles (145) are used. In another example, only black particles (150)are used. Therefore, the present specification contemplates the use ofthese other examples.

In operation, the e-paper printing device (100) passes a sheet ofe-paper across the electrodes (105, 110) causing an erasure of the imageon the e-paper. A voltage controller (165) may cause an electricalcharge to he applied to the charged electrode (110) and cause the groundelectrode to be grounded. As will be described later, the voltagecontroller (165) may also control a corona device (160) such thatelectrical charge applied to the corona device (160) causes the coronadevice (160) to produce a corona sufficient to write to the e-paper.

In one example, the relative movement of the e-paper (115) to theelectrodes (105, 110) may be accomplished through the use of atranslator (170). In the example of FIG. 1, the translator (170) is aroller. Although FIG. 1 shows that e-paper is passed over the electrodes(105, 110), in another example the e-paper printing device (100) maycause the electrodes (105, 110) to pass over the e-paper while thee-paper is left stationary. Therefore, the present specificationcontemplates an e-paper printing device (100) which passes e-paper overan electrode (105, 110), passes an electrode (105, 110) over thee-paper, or combinations thereof so as to erase the e-paper.

As discussed above, according to the example in FIG. 1 as the e-paperpasses over the ground electrode (105), it is shielded from anyelectrical potential, However, as the e-paper begins to pass over thecharged electrode (110), the e-paper experiences an abrupt change from azero field to some maximum field which the charged electrode (110)produces. In one example, the voltage controller (165) may cause thecharged electrode (110) to maintain a constant voltage and thus aconstant electrical field. In another example, the voltage controller(105) may cause the charged electrode (110) to produce a variableelectrical field by applying a variable electrical voltage to thecharged electrode (110).

The maximum field will depend both on the voltage applied to the chargedelectrode (110) as well as the properties of the e-paper such as thecharges of the particles (145, 150). In one example, the time spanbetween applying a zero field to a maximum field is between 20 ms and 50ms.

In addition to the abrupt change in the field produced, the shape of thecharged electrode (110) also provide for better erasing of the image. Asseen in FIG. 1, the charged electrode (110) is shaped such thatelectrical field is gradually reduced as any portion of the e-paper ispassed over it. In one example, the charged electrode (110) has a bentshape such that the radius is around 1 inch. The speed at which thee-paper is passed over these electrodes (105, 110) is about 1 in or 2inches per second. The gradual reduction in the field results in thepreservation of the erased state on the e-paper.

After erasure, the e-paper may then also be written to by passing itover a positive corona device (100). As discussed above, the positivecorona device (160) may selectively apply positive ions to the surfaceof the e-paper, causing one type of pigment (145, 150) to be attractedto the surface (155) of the e-paper (115) thereby causing an image toform on the e-paper (115). In another example, a negatively chargedcorona device may be used instead of the positively charged coronadevice (160) if the c-paper has first been erased via the printingdevice (100) such that the negatively charged particles in the e-paperare already presented closer to the transparent charge receiving layer(125).

FIG. 2 is a block diagram of an e-paper printing device (200) accordingto another example of the principles described herein. In this figure, acurved electrode may comprise two charged electrodes (205, 210); onethat is positively charged and one that is negatively charged. In oneexample, both electrodes (205, 210) are shaped so as to apply a variablefield to the e-paper as the e-paper passes over them. The electricalcharge applied to the charged electrodes (205, 210) may be exclusivelyopposite of each other. If the first charged electrode (205) ispositive, then the second charged electrode (210) is negative and visaversa. Therefore, unlike in FIG. 1, as the e-paper passes over theelectrodes (205, 210) the e-paper (115) is subjected to, for example, anegative electrical field first and then a rapid positive electricalfield as it passes over to the second electrode (210). Both chargedelectrodes (205, 210) are curved such that the e-paper is subjected toboth a gradually increasing negative electrical field and a suddenlyincreasing but gradually decreasing positive electrical field. As thee-paper is subjected to the negative electrical field, little if noeffect will be demonstrated on the image on the e-paper. As the e-papercrosses the gap, however, a double voltage step voltage (from negativeto neutral and from neutral to positive electrical field) is experiencedby the e-paper (115) and the erasing process begins. As the positiveelectrical field is gradually reduced due to the shape of the secondelectrode (210) this will preserve the erased state on the e-paper.

Turning now to both FIGS. 1 and 2, in one example the electrodes (105,110, 205, 210) may be covered with a dielectric material. The dielectricmaterial may be used to prevent arcing between the electrodes (105, 110,205, 210). Additionally, the dielectric material may be used as a spacerto keep a small and accurate gap between the electrodes (105, 110, 205,210) and the e-paper (115).

Additionally, in one example, the electrodes (105, 110, 205, 210) may beformed into a roller. The roller may therefore be used to both providetransport capability of the e-paper as well as the electric field.

In another example, the charged electrodes (110, 210) may be formed intoa single planar electrode and may he used to erase the e-paper (115)using a voltage waveform. In this example, the e-paper (115) may bewritten to by applying a voltage at to the e-paper (115) while thee-paper (115) remains still relative to the electrode. The e-paper maythen be erased (reset) by the application of a voltage waveform to theelectrode at a first rate. The erased state of the e-paper (115) maythen be maintained by applying a gradually decreasing voltage to thecharged electrodes (110, 210) at a second rate. In this example, thefirst rate is relatively faster than the second rate. Alternatively, aseries of alternated finger electrodes may be used to generate multiplewrite/erase cycles as the e-paper is moved through the printer (100,200).

FIG. 3 depicts a waveform (300) used as an erase pulse and applied tothe electrodes (FIG. 1, 105, 110; FIG. 2, 205, 210) as the e-paper ispassed through the printer (FIG. 1, 100; FIG. 2, 200) according to oneexample of the principles described herein. The erase pulse may beinitiated by the erasure electrode (110, 210) as described in FIGS. 1and 2. In this case, as the e-paper (115) approaches the erasureelectrode (110, 210) it experiences a shape rise (305) in electricalfield due to the voltage applied to the erasure electrode (110, 210). Inone example the time (310) that this takes is around 1 ms. The e-paperthen experiences a holding electrical field (315) for a certain lengthof time (320). This length of time may be up to 200 ms. Because theerasure electrode (110, 210) is curved away from the e-paper (115) asthe e-paper (115) passes it, the e-paper (115) experiences a decayingelectrical field (325) for a length of time (330). This length of timemay be anywhere from 10 ms to 0.5 sec.

Using the waveform (300) described above, a sheet of e-paper (115) wastested using the apparatus described in FIG. 4. FIG. 4 is a blockdiagram of an apparatus (400) used to test the e-paper (115) of FIGS. 1and 2 according to one example of the principles described herein. Inoperation, a piece of e-paper (115) is placed between a ground electrode(405) and a excitation electrode (410). Additionally, the apparatus(400) may also comprise a dielectric layer (415) placed between theexcitation electrode (410) and the e-paper (115). The excitationelectrode (410) may have a voltage applied to it according to thewaveform (300) as described in connection with FIG. 3. The results ofboth a writing and erasing pulse are shown in FIG. 5.

FIG. 5 depicts a waveform (500) used as a write and erase pulse and isapplied to the electrodes as the e-paper (115) is passed through theprinter (100, 200) of FIGS. 1 and 2 according to one example of theprinciples described herein. Using the apparatus described in FIG. 4,the e-paper (115) was imaged using alternating writing pulses and erasepulses. Each sharp change in voltage (505, 510, 515) may last around 1ms.

FIG. 5 further comprises a number of photos. Each photo shows theresulting image obtained in the e-paper media after the indicatedtransition for different decay times in the erase pulse. In this case ifthe objective was to erase (i.e., turn e-paper media to white) then thefield is made to rise in less than 100 ms for a low backgroundcondition. As can be seen, at a 2 second rise time the erasure is noteffective at all. With this data and the operating speed of the e-paperprinter (100, 200) the electrode (105, 110, 205, 210) configuration asdescribed and shown in FIGS. 1 and 3 are designed to provide effectiveerasure of the e-paper (115), This example has been provided as a way toquantify the field change rates used to provide an erasure transition.In the examples above with the shaped electrode having stationarypotentials, the temporal electrical field transitions are the result ofthe convolution of the temporally invariant fields at a fixed locationas the e-paper moves relative to the electrodes. It should also be notedthat because the e-paper responds to pulses up to a certain frequency, asuperimposed periodic signal of a frequency higher than this responsetime on top of the stationary potentials would not affect the erasureoperation.

FIG. 6 is a flowchart showing a method of block erasing e-paperaccording to one example of principles described herein. The method maybegin with passing (605) the sheet of e-paper across a curved electrode.As described above, the electrode may have a voltage applied to it inorder to create an electric field. In one example, the e-paper printer(100, 200) may further comprise a roller to translate the e-paperthrough the printer (100, 200) and across the electrode (110, 210), Inanother example, the electrode (110, 210) may be placed on a rollerwhich, when rotated, provides both the translation of the e-paper (115)through the printer (100, 200) as well as apply the electric field tothe e-paper (115).

As the e-paper is passed over the electrode, the electrode initiallyapplies (610) a rapidly increasing electric field to the e-paper. Therapidly increasing electric field may be applied (610) to the e-paper inabout 1 ms. Again, as described above, the polarity of the electricfield applied to the e-paper may depend on the properties, of thee-paper. In one example, the rapidly increasing field may be facilitatedby the use of a ground electrode (105) placed immediately before thecharged electrode (110). In another example, the rapidly increasingfield may be facilitated by the use of a oppositely charged electrode(205) placed immediately before the erasure electrode (210).

As the e-paper is passed (605) over the electrode and the rapidlyincreasing electric field is applied (610), the electric field may begradually decreased (615) to preserve the erased state on the e-paper.

Referring now to FIG. 7, in one example, after the e-paper has beenpassed (705) across the electrode, the electric field is applied (710)to the e-paper, and then gradually decreased (715), a positive coronadevice may selectively apply (720) positively charged ions to thesurface of the e-paper. This creates the image o the e-paper.

The present specification further contemplates the use of a computerprogram product to affect the methods described above. Therefore, in oneexample, the present specification contemplates a computer programproduct for block erasing e-paper, the computer program productcomprising a computer readable storage medium comprising computer usableprogram code embodied therewith, the computer usable program codecomprising computer usable program code to, when executed by aprocessor, create an electrical pulse with the waveform (300) depictedin FIG. 3 during translation of a piece of e-paper (115) across anelectrode. As described above, the waveform (300) rapidly applies anelectric field in about 1 ms. The computer usable program code mayfurther comprise computer usable program code to when executed by aprocessor, gradually decrease the electric field created as the e-paperpasses over the electrode, Because of the curved shape of the electrode,the electric field is gradually decreased as the e-paper continuesthrough the e-paper printer (100, 200).

The specification and figures describe a system and method to blockerase e-paper. The erasing device and printer described herein allows apiece of e-paper to be printed to rapidly without using a negativelycharged corona device to first erase the e-paper. As described above,using a negatively charged corona device to erase the e-paper results inozone being created. Additionally, a negatively charged corona device isunstable resulting in irreproducible e-paper marking or erasure.

Turing now to FIG. 8, a flowchart showing a method (800) ofmanufacturing an e-paper (115) printing device (100, 200) is shownaccording to one example of the principles described herein. The processmay begin by electrically coupling (805) an erasing electrode to avoltage waveform controller. As described above, the erasing electrode(102, 202) may comprise a ground electrode (105) and a charged electrode(110) or oppositely charged electrodes (205, 210). The voltagecontroller (165) may apply a voltage to the electrodes (110, 205, 210)sufficient to erase the e-paper and maintain the erase state of thec-paper as the e-paper is passed over the electrodes (105, 110, 205,210). The method (800) may further include operatively coupling atranslator (170) to the voltage controller (165) such that the voltagecontroller (165) may also cause the e-paper (115) to pass over theelectrodes (105, 110, 205, 210). The voltage controller (165) maycontrol the speed at which the e-paper (115) passes over the electrodes(105, 110, 205, 210). The method (800) may also comprise operativelycoupling a printing device (160) to the voltage controller (165) suchthat the voltage controller (165) may also control when and how theprinter (160) causes an image to be applied to the e-paper (115). Theprinting device (160) may be a positive corona device as describedabove.

The preceding description has been presented to illustrate and describeexamples of the principles described. This description is not intendedto be exhaustive or to limit these principles to any precise formdisclosed. Many modifications and variations are possible in light ofthe above teaching.

What is claimed is:
 1. An e-paper printing system comprising: a set ofelectrodes comprising a number of electrodes to erase a portion ofe-paper as the e-paper moves relative to the set of electrodes in whichthe set of electrodes: causes a first electric field to be applied tothe e-paper with a magnitude of the first electric field increasing at afirst rate sufficiently high to cause the erasure of the portion of thee-paper; and causes a second electric field to be applied to the e-paperwith a magnitude of the second electric field decreasing at a secondrate that is sufficiently low to preserve the erasure of the portion ofthe e-paper.
 2. The e-paper printing system of claim 1, in which thenumber of electrodes of the set of electrodes are each set to differentpotentials which a in average stationary
 3. The e-paper printing systemof claim 2, in which the increase of the magnitude of the first electricfield at the first rate and the decrease in the magnitude of the secondelectric field at the second rate is controlled by: the shape of the setof electrodes; and the speed of the e-paper moving relative to the setof electrodes.
 4. The e-paper printing system of claim 2, in which theincrease of the magnitude of the first electric field at the first rateand the decrease in the magnitude of the second electric field at thesecond rate is controlled by: the differing static potentials set atspatially neighboring electrodes of the number of electrodes; andspatial distances between the neighboring electrodes in the direction ofrelative motion.
 5. The e-paper printing system of claim 3, in which theset of electrodes comprises: a grounded counter electrode; a groundederasure electrode; and a shaped electrode held at an erasing potential:and in which relative motion of the e-paper past the grounded erasureelectrode and then the shaped electrode initially causes the firstelectric field to be applied to the e-paper at the first rate and thencauses the second electric filed to be applied to the e-paper at thesecond rate.
 6. The e-paper printing system of claim 3, in which the setof electrodes comprises: a grounded counter electrode; a first shapedelectrode having a static potential applied to it sufficient to causethe e-paper to be written to; and a second shaped electrode held at astatic potential sufficient to cause the e-paper to be erased; and inwhich relative motion of the e-paper past the first and then the secondshaped electrode initially causes: the e-paper to be subjected to anelectric lied sufficient to write to the e-paper; the first electricfield to be applied to the e-paper at the first rate; and causes thesecond electric filed to be applied to the e-paper at the second rate.7. The e-paper printing system of claim 1, in which the first and secondelectric fields are produced by a temporal variation of potentials atthe set of electrodes while the e-paper is brought within those electricfields.
 8. A method of manufacturing an e-paper erasure devicecomprising: electrically coupling an erasing electrode to a voltagecontroller; the erasing electrode to erase a portion of e-paper; inwhich the erasing electrode is shaped to create a varying gap between acounter electrode so as to cause, during relative motion of the e-paperto the erasing electrode: a first electric field to be applied to thee-paper with the magnitude of the first electric field increasing at afirst rate sufficiently high to cause the erasure of the portion of thee-paper, and at an area downstream where the first electric field isapplied to the e-paper, a second electric field to be applied to thee-paper with the magnitude of the second electric field, decreasing at asecond rate sufficiently low to preserve the erasure of the portion ofe-paper.
 9. The method of claim in which the erasing electrode comprisesa grounded counterelectrode, a ground electrode, and a charged electrodeelectrically coupled to the voltage controller, the ground electrode andcharged electrode creating a gap between them; and in which: the firstelectric field is applied to the e-paper as the e-paper moves relativeto the gap; and the second electric field is applied to the e-paper asthe e-paper moves relative to the charged electrode.
 10. The method ofclaim 9, in which the charged electrode creates an increasing gap awayfrom the counterelectrode as the e-paper moves relative to the chargedelectrode, and in which the second electric field decreases at thesecond rate depending on: the spatial rate at which the chargedelectrode gap increases; and the rate at which the e-paper passes overthe charged electrode.
 11. The method of claim 8, in which: the erasingelectrode comprises a first charged electrode and a second chargedelectrode electrically coupled to the controller; the that electricfield is applied to the e-paper when the e-paper moves relative to thefirst charged electrode; and the second electric field is applied to thee-paper is the e-paper moves relative to the second charged electrode.12. The method of claim 1 in which the first charged electrode and asecond charged electrode are oppositely charged.
 13. The method of claim8, further comprising operatively coupling a translator to thecontroller, in which the translator produces relative motion between thee-paper and the erasing electrode.
 14. The method of claim 8, in which:the first electric field is produced by the controller applying a firstvoltage to the erasing electrode; and the second electric field isproduced by the voltage controller applying a second voltage to theerasing electrode.
 15. The method of claim 8, further comprisingcommunicatively coupling a printing device to the controller to print animage on the e-paper.
 16. A computer program product for erasinge-paper, the computer program product comprising: a computer readablestorage medium comprising computer usable program code embodiedtherewith, the computer usable program code comprising; computer usableprogram code to, when executed by a processor, cause a first electricfield to be applied to the e-paper by a shaped erasing electrode, inwhich the magnitude of the first electric field increases at a firstrate sufficiently high to cause the erasure of a portion of the e-paper:and computer usable program code to, when executed by a processor, causea second electric field to be applied to the e-paper by the shapederasing electrode, in which the magnitude of the second electric fielddecreases at a second rate sufficiently low to preserve a the erasure ofthe portion of e-paper area.
 17. The computer program product of claim16, further comprising: computer usable program code to, when executedby a processor, cause the creation of first electric field by causing avoltage controller to apply a first voltage to a first electrode of theshaped erasing electrode; and computer usable program code to, whenexecuted by a processor, cause the creation of the second electric fieldby causing the voltage controller to apply a second voltage to a secondelectrode of the shaped erasing electrode.
 18. The computer programproduct of claim 16, in which the shaped erasing electrode comprises aground electrode and a charged electrode and in which: the firstelectric field is applied to the e-paper by causing relative motionbetween the e-paper and a gap created between the ground electrode andthe charged electrode; and the second electric field is applied to thee-paper by causing relative motion between the e-paper and the chargedelectrode.
 19. The computer program product of claim 18, in which therelative motion between the e-paper and the ground and chargedelectrodes is accomplished by causing a roller to push the e-paper. 20.The computer program product claim 16, in which the first rate is higherthan the second rate.